JP3224477B2 - Image forming apparatus and charging method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus using a charging roller or other contact-type charged body, for example, a copying machine, a printer, a facsimile, or an image forming apparatus applied as a process cartridge of these apparatuses and the image forming apparatus. The present invention relates to charging of a photoconductor constituting a forming apparatus.

[0002]

2. Description of the Related Art Conventionally, respective process means of exposure, development, transfer, cleaning (removal of residual toner), charge elimination and charging are arranged on the outer peripheral surface of a photosensitive drum, and an image is formed by a predetermined electrophotographic process. Electrophotographic apparatuses based on the so-called Carlson process are well known.

The charging means used in this type of apparatus is generally a corotron type in which a high voltage is applied to a thin tungsten wire to perform corona discharge, or a charging means in which a voltage of several hundred volts is applied to a conductive roller to contact and charge a photosensitive drum. (Japanese Unexamined Patent Publication (Kokai) No. 5-297690, etc.), a device in which a voltage is applied to a conductive brush to charge while making contact with a photoreceptor drum, and a brush is formed by attaching magnetic particles to a conductive sleeve in which a magnet is inserted. A so-called particle charging method has also been proposed, in which a magnetic brush in the form of a brush is rubbed against a photosensitive drum and a charging bias is applied to a group of magnetic particles via a sleeve to perform charging (JP-A-59-133569 and others).

However, since the corotron method uses a high voltage and has many safety and environmental problems such as generation of ozone, the charging roller, the charging brush, and the charged particles are brought into contact with the photosensitive drum. A so-called contact charging method, in which charging is performed while applying a charging bias to the photoreceptor drum via these contact charging members, has been attracting attention. Since charging is performed in a state in which the photosensitive drum is in contact with the photosensitive drum, residual toner adhered to the photosensitive drum after transfer and paper powder adhered during transfer adhere to the charged body, and uneven charging and smooth charging can be performed. May not be.

For this reason, a cleaning blade is generally arranged upstream of the charging position in the rotation direction of the photosensitive drum.
Although the cleaning blade is used to remove residual toner, in an apparatus using an OPC drum as the photosensitive drum, the OPC drum is made of an aluminum pipe made of a relatively soft organic resin layer. If the contact charging member is used by rubbing the rotating OPC drum together with the blade for a long period of time on the rotating OPC drum, the surface of the photosensitive layer gradually wears, The charging characteristics change due to the change in equivalent capacitance. In particular, when a DC bias is used as the charging bias applied to the contact charging member, a change in the capacity of the photoconductor is greatly affected.

That is, when the DC bias power supply 43, the charging roller 4, the photosensitive drum 1, and the ground potential E are connected in series as shown in FIG. 4A, it is clear from the equivalent circuit shown in FIG. As described above, when the film thickness of the photosensitive layer 1a decreases due to long-term use, the DC current flowing to the charging roller 4 increases in proportion to the photosensitive member sensitivity, and the surface potential of the outer surface of the photosensitive member 1 increases. As a result, the development contrast and the development density increase, and a sufficient reverse contrast with respect to the background potential cannot be obtained, so that a so-called fog occurs.

Conventionally, in order to solve such a drawback, a current flowing through the photosensitive member 1 or a DC voltage corresponding to the layer thickness is detected and applied to the charging member 4 based on the detected current (voltage). A technique for correcting and controlling a DC voltage or a DC current (Japanese Patent Laid-Open No. 5-307315) has been proposed.

[0008]

However, in the case of the OPC drum, the amount of film reduction from the start of operation to the use limit time, in other words, since the charging capacity of the photosensitive member 1 is large, the OPC drum can be controlled over a wide control range. Constructing a simple circuit leads to complicated circuit configuration and unnecessary increase in manufacturing cost. In addition, the current and the like flowing through the photoreceptor 1 do not always fluctuate in proportion to the film thickness alone, but also fluctuate due to environmental factors such as temperature and humidity in the apparatus. However, accurate control is not always possible, which is not a good idea.

In particular, in the case of using an OPC drum to the photosensitive drum 1, the photosensitive layer thickness has a capacitor function, for charging the results drum surface, the C ₁ shown in FIG. 4 (B) the charge voltage V corresponds to that charge and thus the surface potential Vd flowing through the photoreceptor in accordance with a change in the capacitance of C _1, specifically the surface potential Vd As the film thickness becomes thinner to increase. The charging roller is intended to change the resistance R ₁ by temperature and humidity. Therefore, the increase in complication of the manufacturing cost of the circuit configuration as described above to attempt to precisely control the two heterogeneous variables of the charging roller VR ₁ having a resistance function and the photoreceptor VC ₁ having a capacitor function In addition to the connection, there is noise such as contamination of the charging roller and the photosensitive drum, and precise control is difficult.

For this reason, the current detection sensor normally detects only the film thickness reduction of the photoreceptor and controls the charging voltage by using the current detection sensor. There is no defense against environmental changes in the rollers. In particular, the charging current is relatively large when approaching the endurance life due to the film decrease, in other words, when the charging function is increasing, so that the surface potential fluctuation due to environmental fluctuations is likely to increase, especially at low temperature and low humidity. (In the case of constant voltage) has a large effect. On the other hand, at the beginning of the operation of the photoconductor drum, that is, while the photoconductor film thickness is large, the charging function is low, in other words, the charging current is low, and as a result, problems caused by environmental fluctuations can be reduced.

[0011] In view of the disadvantages of the prior art, the present invention provides
An invention capable of suppressing the fluctuation of the surface potential caused by the fluctuation with a simple circuit configuration in any case of the film thinning of the photoreceptor or the environmental fluctuation and performing stable and high-quality charging and image formation over a long period of time. The purpose is to provide.

[0012]

The present invention is suitably applied to an apparatus using an OPC photosensitive member as a photosensitive member, a DC bias as a charging bias, and a charging roller as a charging member. Not only the roller, but also any of a particle charging system and a brush charging system can be applied. That is, the present invention includes an image forming apparatus that includes a charged body that is arranged in contact with a photoconductor, and performs image formation while uniformly charging the photoconductor via a DC charging voltage applied to the charged body. Using an OPC photoconductor, a voltage upper limit unit and a voltage lower limit unit that limit a DC charging voltage applied to the charger to a predetermined width range, and detect a charging current flowing through the photoconductor within the predetermined width range, Means for generating a detection voltage proportional to the increase or decrease of the charging current; and a means for generating a detection voltage based on a preset reference voltage when the detection voltage reaches a lower limit voltage level or an upper limit voltage level. A reference charging voltage generating means for generating the charging voltage to be applied; and adjusting the DC charging voltage based on the detection voltage when the detection voltage is between the lower limit voltage level and the upper limit voltage level. Performs constant current control of the current flowing to the photosensitive member while, a constant-current control means, it is characterized in that for controlling the voltage applied to the photosensitive member on the basis of the detection voltage. In the present invention, the reason why the photoreceptor is limited to the OPC photoreceptor is that a-Si and other inorganic photoreceptors have a stronger resistance function than a capacitor function and basically have a different control from an apparatus using an OPC. there is a need Karadea
You.

The constant current control means detects a charging current flowing through the photoreceptor within the predetermined width range and generates a detection voltage corresponding to the charging current, and a DC charging voltage based on the detection voltage. It is preferable that the constant current control of the current flowing through the photoconductor is performed while the adjustment is made. Also, the upper limit or lower limit voltage level obtained by each of the voltage upper limit limiter and the lower limit limiter is not necessarily required to be fixed, and the upper limit or lower limit voltage level can be corrected based on environmental conditions. Is also good. As such a configuration, for example, means for detecting a charging current flowing through the photoreceptor and generating a detection voltage proportional to an increase or decrease in the charging current is provided, and each of the upper limit and the lower limit is limited based on the detection voltage. It is preferable that the upper or lower limit voltage level obtained by the means can be corrected.

As a preferable charging method for performing such control, in the charging method of an image forming apparatus for uniformly charging the photosensitive member via a DC charging voltage applied to the charged member arranged in contact with the photosensitive member, detecting a DC charging voltage to be applied to the body as a detection charging voltage, the detected charging electric
When the pressure reaches the lower limit voltage level or the upper limit voltage level, a reference charging voltage is applied to the photoconductor based on a preset reference voltage, and the detected charging voltage is the difference between the lower limit voltage level and the upper limit voltage level. If it is in the middle,
While adjusting the DC charging voltage based on the charging voltage a constant current control of the current flowing to the photosensitive member, the detection zone
A voltage applied to the photoconductor is controlled based on an electric voltage . The charging voltage the is generated based on a preset reference voltage need not be fixed, as shown in FIG. 5, as shown in FIG. 6, the detection charge collector
As described above , the correction may be performed based on the pressure , and the upper limit or lower limit charging voltage level corresponding to the environmental change may be set.

[0015]

According to the present invention, as shown in FIG. 5, the charging voltage to the charging roller is basically reduced both in the early stage of operation when the film thickness is large and when the film thickness is reduced due to long-term use. Irrespective of the reduction in the film thickness of the photoreceptor, a fixed voltage is constantly applied to the charging roller using the lower limit voltage or the upper limit voltage of the voltage level range substantially corresponding to the reduction in the intermediate film.

[0016] That is, the above OPC photosensitive member is worn by the image forming as, for capacitance C ₁ as the film reduction occurs is increased, by increasing the charging voltage in inverse proportion to this in the prior art , by increasing the surface potential in other words to try to maintain the VC ₁ constant.

[0017] When the environmental change occurs in this state, the charging roller resistance value variation of the resistance V _R1 the current flowing through the photosensitive member (charging current) is varied occurs, the VC ₁ occurs is a change in the surface potential Vd if words Kaere Fluctuations occur. So although possible to suppress the fluctuation of the photosensitive member VC ₁ due to the environmental change by the constant current control is disclosed in the prior art, the film thickness is reduced by long-term use photoconductor thickness of the original operation of a thick state Performing constant current control in response to the above-described environmental fluctuations while performing current or voltage control over a wide range up to the state described above complicates not only the circuit configuration but also the control thereof. .

Therefore, the present invention solves the above-mentioned drawback by limiting the charging voltage applied to the charging member to a predetermined width range as shown in FIGS.

[0019] That is the effect of the present invention to be described with reference to FIG. 5, in the conventional art, in order to maintain the charge capacity VC ₁ of the photosensitive member at a constant, as indicated by a broken line shown in FIG. 5 (B) ,
The charging voltage from C ₁ by film reduction is to have decreased it is necessary to increase inversely with. However, in the present invention, in the initial stage of operation, the upper limit voltage obtained by increasing the conventional charging voltage at the film thickness in advance at the film thickness is used, and the upper limit voltage is constantly controlled without voltage control until the film thickness decreases by a predetermined thickness. Is applied with a fixed voltage.
As a result, VC ₁ becomes small at the beginning of operation,
Conversely even when the resistance value change of the charging roller resistance V _R1 due to environmental variations relative which can be suppressed. Also, by increasing the charging voltage to a level equivalent to the lower limit level of the reduction of the intermediate film, the development contrast and the development density are relatively increased, and the contrast and the development are the same as the charging state of the reduction of the intermediate film described later. The concentration can be obtained, and the variation between the two can be suppressed. In this case, more precise control is possible by correcting the upper limit voltage according to environmental conditions as shown in FIG.

Next, when the film thickness has been sufficiently reduced due to long-term use, on the contrary, the charging roller is charged to the charging roller as shown in FIG. A constant voltage is applied constantly. As a result, V
C ₁ is increased, because the surface potential becomes lower equivalent extent as the upper limit level of the reduced intermediate film as shown in FIG. 5 (B), to obtain the same contrast and development density and the charged state of the reduced intermediate layer As a result, not only the variation between the two can be suppressed, but also a sufficient reverse contrast with respect to the background potential can be obtained, and a reduction in fog can be prevented. In this case as well, more precise control is possible by correcting the upper limit voltage according to environmental conditions as shown in FIG. Note that only the lower limit voltage level may be corrected according to environmental conditions, and the upper limit voltage may be a fixed voltage.

Finally, in the state where the intermediate film is reduced between the lower limited voltage level and the upper limited voltage level, the present invention performs constant current control of the current flowing through the photoreceptor by adjusting the charging voltage. thereby achieving suppression of variation in charging capacity VC _1.

As a result, as shown in FIGS. 5 (B) and 6 (B), in both the initial stage of operation and after long-term use, the voltage was brought closer to the voltage level corresponding to the surface potential (charging voltage) in the reduction of the interlayer film. On the other hand, in the step of reducing the interlayer film, constant current control is performed in accordance with environmental conditions to always bring the surface potential closer to a predetermined voltage level region at the center, thereby eliminating the drawbacks of the above-mentioned prior art.

[0023]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just.

FIG. 2 shows an image forming apparatus to which the present invention is applied.
In particular, a basic configuration diagram of a process unit around the photosensitive drum 1 of the printer is shown, and an electricity removing means 2 including an LED unit 8, a developing unit 60, a transfer roller 7, a cleaning blade 3, and an eraser is arranged along the drum rotating direction (clockwise). , A charging roller 4 is disposed, and as is well known, the charge removing means 2
After the charge is removed, the exposure latent image is written by the LED unit 8 on the photosensitive drum 1 uniformly charged by the charging roller 4, and the toner image is visualized by the developing unit 60 by reversal development of the exposure latent image, After transferring the toner image to the recording medium 10 by the transfer roller 7, the residual toner is removed by the cleaning blade 3. The residual toner removed by the cleaning blade 3 is stored in a waste toner bottle (not shown) by a screw (not shown).

Next, the respective process means will be described. The photoconductor drum 1 uses an OPC drum 1 (organic photoconductor) having a diameter of 30φ and a negative charging polarity, and is configured to be rotatable at a predetermined peripheral speed in the direction of the arrow. The thickness (the total thickness of GGL, CTL, etc.) of the photoconductor layer 1a of the photoconductor drum 1 is set to 25 μm.

As is well known, the LED units 8 are
It consists of an LED head with D elements arranged and a focusing lens,
An exposure latent image corresponding to image information can be written on the photosensitive drum 1.

The developing unit 60 comprises a developing container 61 containing a multi-component developer composed of a carrier and a toner, and a developing roller 62 containing a fixed magnet assembly (not shown). A DC development bias power supply 65 of -450 V is connected to perform development by low electric field reversal development.

As the carrier, a carrier is used in which conductive fine particles are fixed on the surface of carrier base particles in which a magnetic substance is uniformly dispersed in a binder resin, and has a magnetic force of 5 kOe (Oersted). The maximum magnetization in a magnetic field is 55 to 80 emu / g, and the average center particle size of the carrier is 3
A developer having a particle size distribution of 5 μm, particularly containing 15 wt% or more of particles of 35 μm or less is used.

As the toner, a normal high-resistance or insulating toner is used. For example, a magnetic substance is added to a binder resin, a coloring agent, a charge control agent, an offset preventing agent, etc., and the average central particle size is 5 to 15 μm. The carrier and the toner are configured as the front and rear magnetic toners, and an appropriate mixing ratio of the carrier and the toner is set to, for example, 85 to 90:15 to 10% by weight.

The transfer roller 7 has a resistivity of 10 ⁵ Ω · cm.
Using the following conductive elastic roller, specifically, a urethane rubber roller, the transfer bias 70 is set to +250 V which is opposite to the surface potential of the photoconductor 1a and the polarity of the toner image charge.

On the other hand, the cleaning blade 3 is formed by attaching a plate-like polyurethane elastomer material having a wedge-shaped cross section to a support member (not shown), and having a corner at the front end of the photosensitive drum 1.
Are arranged so that they are almost in line contact.

The charging roller 4 is driven and rotated in synchronism with the photosensitive drum 1 to mold a polyurethane rubber to which a conductive component has been added around a 6 mm stainless steel core made of a solid shaft made of stainless steel. It is formed by applying a nylon resin coating on the surface. If necessary, the surface layer of the rubber layer of the charging roller 4 may be subjected to a curing treatment.

A charging bias control circuit is connected to the metal core, and a cleaning roller 5 is arranged in contact with the back side of the charging roller 4.

In the cleaning roller 5, after a rubber layer is coated on the surface of the cored bar, a string-like body made of a chemical fiber material, preferably a thick yarn-like chemical fiber or a long fiber is implanted on the surface. Is wound in a spiral shape with different circumferential directions left and right from the center position, and by the rotation of the cleaning roller 5, the attached matter on the roller 5 can move from the center side to the shaft end side. Is formed.

FIG. 1 is a circuit diagram of the charging bias control circuit. To briefly explain the structure, reference numeral 20 denotes a high-voltage transformer comprising a primary winding L _I and secondary windings Lo and Ls. line L _I predetermined DC voltage supply Vi at one end of,
The other end is connected to the emitter of the transistor Q1 whose collector is grounded.

Numeral 30 denotes a PWM control circuit which comprises a triangular wave generating circuit 31 and an operational amplifier 32 in which a triangular wave from the generating circuit 31 is introduced to a positive input terminal.
Is connected to the base side of the transistor Q1. On the side of the secondary winding Lo, a constant current circuit 25 for performing constant current control while smoothing the secondary winding side voltage Vo is formed. (Roller). The circuit is connected to the secondary terminal rectifier diode D ₁ ,
A charging roller 4 via a resistor R ₁ load of the photosensitive drum 1 is connected, and the two capacitors C ₁ between the terminals of the resistor, C ₂ are connected in parallel, the winding Lo - connected to the terminal side Have been. A current voltage (I) is applied between the negative terminal and the ground potential.
/ V) Conversion resistor I / V is connected.

The detection voltage corresponding to the charging current extracted from the conversion resistor I / V is connected to the + terminal of the inverting circuit 34 via the limiting resistor R _{3 and} to the output terminal of the lower limiter 35 via the diode D _2. , Respectively.
The inverting circuit 34 slices the triangular wave applied from the + terminal side by applying the feedback voltage obtained by inverting the detection voltage to the − terminal side of the operational amplifier 32,
ON / O having a pulse width corresponding to the slice level
The FF signal is applied to the base of the transistor Q _1.

A reference voltage setting circuit 341 is connected to the negative terminal of the inverting circuit 34 as necessary, and a constant current circuit that always maintains a constant current by comparing the detected voltage with the reference voltage set by the circuit 341 is provided. Constitute.

On the other hand, a diode D ₃ is connected to the secondary winding Ls.
And consists capacitor C _3, the circuit 27 for generating a detection voltage winding Ls voltage by smoothing is configured,
The circuit 27 applies a detection voltage proportional to the winding Ls to the + input terminal of each of the upper limiter 36 and the lower limiter 35. Then, the upper limiter 36 and the lower limiter 3
The reference voltage setting circuit 3 is connected to each of the-input terminals of
51 and 361 are connected.

Next, the operation of the circuit will be described with reference to the voltage waveform diagram shown in FIG. Since this circuit is a flyback system based on PWM control, the triangular wave is compared (sliced) with the output voltage of the higher one of the inverting circuit 34 and the upper limiter 36 in the operational amplifier 32 constituting the PWM control circuit 30. ON corresponding to the slice width
/ OFF pulse is applied to the base of the transistor Q _1. Then, based on the ON / OFF pulse signal from the operational amplifier 32, the transistor Q ₁
The collector is turned ON, the winding primary side L _I {(1 /
2) Energy of L _I · i ² ｝ (L _I : winding inductance · i ² : primary average current) is accumulated, and when the transistor Q ₁ is turned off, energy is passed through the secondary side rectifier diode D _1. is released, the counter electromotive voltage Vp is generated between the emitter / grounded transistor Q ₁ if words words, transformer 2
Voltages Vo and Vs proportional to the windings are generated between Lo and Ls, which are the secondary windings of 0.

At this time, since L _I is a fixed inductance, the primary output Vp is varied by varying the current i _max of the primary winding. Vp = (i _max ) L _I = ｛(2 · i · T _on ) / (T)｝ L _I 1) T: pulse period T _on : pulse ON width Therefore, Vp is proportional to pulse ON width T _on. It will increase or decrease. The relationship between the primary output Vp and secondary side output Vo is _{Vp = Vi + (n 1 /} n 2) Vo ... 2) Vi: Input Voltage n _1: the primary winding L _I number n _2: secondary side The number of windings Lo.

Accordingly, Vo forms a rectangular pulse-like alternating voltage in proportion to (n ₁ / n ₂ ), but the secondary-side output Vo is smoothed by the capacitors C ₁ and C ₂ , and almost has a peak. A DC voltage V corresponding to the voltage is applied to the roller (load).

In the initial state of operation in which the thickness of the photosensitive drum 1 is large, the charging current flowing through the photosensitive drum 1 is small, and accordingly, the charging current including the charging roller 4 decreases. The charging current is converted by a conversion resistor I / V into a detection voltage corresponding to the charging current. After the detection voltage is inverted by an inversion circuit 34, the operational amplifier 3
2 is input.

The slice level for slicing the triangular wave in the operational amplifier 32 is vertically in response to variations in the feedback voltage, and the base of the transistor Q ₁ the ON / OFF signals of varying pulse ON width T _on commensurate to the displacement movement Is applied. Then, in order the primary output Vp is increased or decreased in proportion to the pulse ON width T _on, when the charging current decreases, and decreasing the pulse ON width T _on, proportional to the output voltage V is charged current in response thereto And the detection-side secondary-side voltage Vs correspondingly decreases.

When the detection-side secondary voltage Vs falls below the lower-limit reference voltage level Sv _L , the lower-limit limiter 35 and the conversion resistor I / V are connected in parallel via the branch 352, whereby the inverting circuit 34, the lower limit voltage _VL on the secondary output side becomes V _L § {(1 / Sv _L ) + (1 / FB)} = {(Sv _L + FB) / S
v Output voltage V _FB corresponding to _L · FB｝ and one side corresponding to the detection voltage
Corresponds to FB. Therefore, V _L is _equal to V _FB by (1+ (Sv _L
/ FB)) times the voltage is boosted. Since the lower limit voltage _VL output to the load changes in proportion to the fluctuation of the FB voltage, that is, the charging current, the lower limit voltage _VL can be adjusted according to environmental fluctuations. Therefore, more accurate adjustment can be performed.

When the photosensitive drum 1 is used in a predetermined amount, the secondary voltage Vs for detection is changed from the reference voltage level Sv _L of the lower limiter 35 to the reference voltage level Sv of the upper limiter 36.
v when within range of _U control as follows is performed. First, the fluctuation of the charging current is converted into a detection voltage corresponding to the fluctuation current by the conversion resistance I / V, and is input to the operational amplifier 32 via the inverting circuit 34. In the operational amplifier 32, the slice level for slicing the triangular wave rises and falls in response to the change in the F / B voltage, and the pulse O corresponds to the change.
An ON / OFF signal in which the N width _Ton changes varies with the transistor Q
₁ is applied to the base side.

As shown in the above equations (1) and (2), the primary output Vp and the secondary output Vo increase and decrease in proportion to the pulse ON width T _on . The pulse ON width _Ton decreases, and in response to this, the secondary-side smoothed output V acts in a downward direction, in other words, in a direction to suppress the charging current. Suppress and a constant current flows. On the other hand, when the charging current decreases, the pulse ON width _Ton increases, and the secondary side output V
Works in the direction in which the charging current increases, whereby even if there is a fluctuation in the charging current, in other words, a change in the environment of the charging roller, the load voltage is adjusted while adjusting the load voltage in response to the fluctuation. A current will flow.

When the film thickness of the photosensitive drum is greatly reduced due to long-term use, the charging current flowing to the photosensitive drum increases, and the charging current is reduced by the conversion resistance I / V.
Is converted into a detection voltage corresponding to the charging current, and the detection voltage is inverted by an inverting circuit 34, and then input to an operational amplifier 32, where the pulse ON width is inversely proportional to the increase in the charging current. _Ton decreases, and the output voltage V correspondingly increases in proportion to the charging current, and the secondary voltage Vs for detection also increases correspondingly.

[0049] Then, when the detecting secondary-side voltage Vs becomes equal to or higher than the reference voltage level Sv _U of upper limiter 36,
The reference voltage level Sv _U with the feedback voltage FB than the inversion circuit 34 is input to the operational amplifier 32, the secondary winding Lo side triangular wave slice level (Sv _U + F
B) a can be obtained an upper limit voltage V _U corresponding. The upper limit limiting voltage V _U is sensed voltage, i.e. in order in proportion to the variation of the charging current varies minutely, to the upper limit limit voltage V _U also can be adjusted also correspond to the environmental change, More accurate adjustment is possible.

In this case, a reference voltage setting circuit 341 is connected to the-terminal side of the inverting circuit 34 as necessary, so that when the detection voltage exceeds the reference voltage set by the circuit 341, the feedback voltage FB becomes an operational amplifier. 32
To the upper limit voltage V _U from the upper limiter 36
Is applied to the negative terminal side of the operational amplifier 32 to generate a fixed slice level.

[0051]

As described above, according to the present invention, the fluctuation of the surface potential due to the fluctuation can be suppressed with a simple circuit configuration, regardless of the film thickness of the photoreceptor or the environmental fluctuation, and stable over a long period of time. In addition, high quality charging and image formation can be performed. And so on.

[Brief description of the drawings]

FIG. 1 is a control circuit of a charging voltage applied to a charging roller according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an image forming apparatus applied to the present invention.

FIG. 3 is a waveform chart showing voltage levels in the circuit of FIG.

FIGS. 4A and 4B are a basic configuration diagram showing a charging application state on a charging roller and a photosensitive drum, and an equivalent circuit thereof.

FIG. 5 is a graph (A) showing a relationship between a charging voltage level and a load fluctuation with a fixed upper or lower charging voltage level obtained by respective upper and lower limit means, and a graph showing surface potential and environmental fluctuation. (B).

FIG. 6 is a graph (A) showing a relationship between a charging voltage level and a load variation in which an upper limit or a lower limit charging voltage level obtained by each of an upper limit or a lower limit is changed according to environmental conditions; It is a graph figure (B) shown.

[Description of Signs] 1 Photoconductor (Photoconductor drum) 1a Photoconductor 4 Charged body (Charging roller) 43 Charging bias power supply

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/02 102 G03G 21/00 398

Claims (4)

(57) [Claims] 1. An image forming apparatus, comprising: a charged member disposed in contact with a photosensitive member, wherein an image is formed while uniformly charging the photosensitive member via a DC charging voltage applied to the charged member; Using an OPC photoconductor, a voltage upper limit unit and a voltage lower limit unit that limit a DC charging voltage applied to the charger to a predetermined width range, and detect a charging current flowing through the photoconductor within the predetermined width range. Means for generating a detection voltage proportional to the increase or decrease of the charging current; and said charging applied to the photoconductor based on a preset reference voltage when the detection voltage reaches a lower limit voltage level or an upper limit voltage level. Reference charging voltage generating means for generating a voltage, and when the detection voltage is between the lower limit voltage level and the upper limit voltage level, adjust the DC charging voltage based on the detection voltage. Performs constant current control of the current flowing to want the photosensitive member, and a constant-current control means, the image forming apparatus characterized by controlling the voltage applied to the photosensitive member on the basis of the detection voltage. 2. The image forming apparatus according to claim 1, wherein the lower limit voltage level and the upper limit voltage level can be corrected and set. 3. A charging method for an image forming apparatus for uniformly charging a photosensitive body via a DC charging voltage applied to a charged body arranged in contact with the photosensitive body, wherein the DC charging voltage applied to the charged body is detected. charging voltage <br/> to detect, the reference charging voltage is applied to the photosensitive body based on a preset reference voltage when said detection charging voltage reaches the lower limit voltage level or the upper limit voltage level, When the detected charging voltage is between the lower limit voltage level and the upper limit voltage level, perform constant current control of a current flowing through the photoconductor while adjusting a DC charging voltage based on the detected charging voltage , A charging method for an image forming apparatus, comprising: controlling a voltage applied to the photosensitive member based on a detected charging voltage . 4. A lower limit voltage level of the charging voltage or
4. The charging method according to claim 3, wherein the upper limit voltage level is corrected according to environmental fluctuation.